Our present invention relates to an apparatus for producing a spun-bond web from synthetic resin filaments.
In general, the production of a spun-bond web involves the emission from a spinneret or spinning head of a curtain of synthetic resin filaments which are collected on an endless deposition belt through which air is drawn by a suction device located below the upper pass of the continuously moving belt. In the deposition region, the filaments deposit in intertwined loops and bond together to form the web. Below the upper pass of the fluid-permeable or sieve belt, a suction device has generally a rectangular inlet which extends the full width of the belt and confines the suction zone to a region substantially immediately below the descending curtain of the synthetic resin filaments.
An apparatus of this type is described, for example, in German patent document DE 43 12 419 C2 and in the corresponding U.S. Pat. No. 5,460,500. The flow and pressure conditions in the web-forming and filament-deposition region are generally controlled only by varying the setting of the suction blower which forms the mechanism for drawing the air through the belt.
It is the principal object of the present invention to provide a relatively simple system which facilitates control of the parameters with which air is drawn through the web forming on the collection belt and through that belt to thereby increase the versatility of the apparatus.
It is a more specific object of the invention to provide an apparatus which can more easily influence the spun-bond web formation, afford greater variability of the product made, and in general, improve a spun-bond product produced by an apparatus of the type described.
It is also an object of the invention to provide an improved apparatus for producing a spun-bond web with better adjustability of the suction, flow and pressure conditions in the web formation region and for introducing greater variability in these parameters.
A further object of our invention is to provide a spun-bond producing apparatus which represents an advance over earlier apparatus for the production of spun bond.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, by providing along both longitudinal edges of the suction intake of a spun-bond producing apparatus of the type described, respective baffle flaps which are pivotally mounted along these edges, extend the full width of the upper pass of the belt and are tiltable individually (independently) or together. More particularly, an apparatus for producing a spun-bond web according to this invention can comprise:
means including a spinneret for producing a descending curtain of thermoplastic synthetic resin filaments;
an endless fluid-permeable belt having an upper pass located below the spinneret for collecting the filaments and forming a spun-bond web therefrom;
a suction device below the upper pass of the belt having an elongated inlet extending transversely to the upper pass of the belt and below the upper pass for drawing air through the upper pass of the belt and the filaments downwardly onto the upper pass of the belt, the inlet having a pair of opposite longitudinal edges; and
a respective baffle flap pivotally mounted at each of longitudinal edges an extending from the respective longitudinal edge substantially to the upper pass of the belt over an entire length of the inlet and swingable to vary the draw of air through the belt.
The invention is based upon our discovery that a significant increase in the variability of the flow and pressure conditions in the deposition region or web-forming regions can be achieved by varying the shape and width of the suction passage intake below the upper pass of the belt. This is achieved in a simple manner, according to the invention by swingable baffles which can be swung toward and away from one another or swung independently to various positions. In this manner both the size and position of the intake with respect to the underside of the upper pass of the belt can be varied within wide ranges.
In a preferred embodiment of the invention, the two flaps are adjustable independently from one another and for that purpose each of the flaps may be provided with a respective actuator.
The flaps can be of solid-wall or perforated construction and it has been found to be advantageous, in some cases, to provide a combination of a solid-wall or nonperforated flap on one longitudinal edge and a perforated flap on the other longitudinal edge.
The use of perforated flaps not only allows the upper edges of the flap to control the width and position of the intake, but also induces flow through the perforations which affect the character (turbulence, etc.) of the airstream adjacent the upper pass of the belt.
To avoid undesired air flow, it has been found to be advantageous to provide upper edges of the flaps with respective round sections which can, if desired, actually engage the underside of the belt.
In all cases it has been found to be desirable, in addition, to provide the blower as an adjustable capacity blower.